The retroreflective security films disclosed in U.S. Pat. No. 3,801,183 (Sevelin) provide many features making them well-suited for use as security overlays which can be laminated over a document or portions thereof. Such films are commonly used on such documents as identification cards, driver licenses, or documents of title, providing means for authenticating the documents as well as means for readily detecting tampering or attempted tampering therewith. Typically, such films are made with reflective layers which are substantially transparent in diffuse light conditions, thereby permitting the information on the document surface to be easily read. Commonly, the entire surface of the film has some level of retroreflection. Typically, any penetration of the film is disruptive to retroreflection by the film and is thus readily apparent under retroreflective viewing conditions, thereby providing means for enabling detection of tampering. Legends or patterns of enhanced retroreflection can be provided as desired in the form of logos, special messages, or other images to provide means for authentication as well as enhanced means for detection of tampering.
U.S. Pat. No. 4,099,838 (Cook et al.) discloses a retroreflective sheet material which carries retroreflective legends provided by a dielectric mirror wherein the mirror is patterned so that the reflectivity from the mirror exhibits a pattern of contrasting colors. The patent teaches that security films of the type disclosed in U.S. Pat. No. 3,801,183 may be made with such patterned reflectivity.
Retroreflective security laminates have come into widespread use, due in large part to the high degree of security they can provide. In order to make complete use of the full potential of their utility, they must be verified under retroreflective conditions, e.g., with a flashlight or specialized device such as a retroviewer such as disclosed in U.S. Pat. Nos. 3,767,291 (Johnson) and 3,832,038 (Johnson).